With the development of wireless communications technologies, there are higher requirements for communication rate and communication quality. After a relay node (RN, Relay Node) is introduced into the 3rd Generation Partnership Project (3GPP, 3rd Generation Partnership Project) Long Term Evolution Advanced (LTE-Advanced, Long Term Evolution Advanced) standard, the problem is effectively solved by using the RN to perform backhaul transmission, and the RN can expand cell coverage, improve cell capacity, and make cell throughput uniform.
When an RN is used as a network node to perform cell coverage, the RN communicates with a base station (eNB, Evolved Node Base station) and a user equipment (UE, User Equipment) under the coverage of the RN in a time division mode. To ensure that a UE in the 3GPP Release-8 (Release-8) standard is not affected when accessing a network, a subframe where a communication link between the RN and the eNB, that is, a relay link, is located is configured as a multimedia multicast broadcast single frequency network (MBSFN, Multimedia Broadcast multicast service Single Frequency Network) subframe, the first 1-2 orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing, OFDM) symbols of the MBSFN subframe are used for the RN to communicate with the UE under the coverage of the RN, while the remaining OFDM symbols may be used for the RN to communicate with the eNB.
However, while the eNB sends a physical downlink control channel (PDCCH, Physical Downlink Control Channel) (1-4 OFDM symbols) to the UE under the coverage of the eNB, the RN also sends a physical downlink control channel PDCCH (1-2 OFDM symbols) at the same time, so the RN cannot receive the PDCCH of the eNB, and the PDCCH of the RN and the PDCCH of the eNB may be of different lengths, which will affect the time when the eNB is capable of sending a PDCCH or a physical downlink shared channel (PDSCH, Physical Downlink Shared Channel) to the RN or the time when the RN is capable of receiving the PDCCH or the PDSCH, thereby affecting resources used on the relay link. In addition, since the RN needs to perform state conversion from a receiving state to a sending state or from a sending state to a receiving state when changing from communicating with the UE under the RN to communicating with the eNB, and the RN cannot receive or send downlink information within the state conversion time, the state conversion time is an idle time/guard time, and the existence of the state conversion time also affects the resources used on the relay link.
In the prior art, to enable the RN to share the PDCCH of the eNB with the UE under the coverage of the eNB, the RN generally offsets an RN frame forward relative to an eNB frame. As shown in FIG. 1, an offset of the RN frame relative to the eNB frame is: the length 1 of a PDCCH of the MBSFN subframe where the relay link of the RN is located+a first idle time 2, in which the idle time 2 includes the state conversion time of the RN. The RN frame will ignore the last several OFDM symbols (equivalent to the offset of the RN frame relative to the eNB frame) of the eNB frame.
The resources used on the relay link (a relay_physical downlink shared channel R_PDSCH) after the RN frame is offset relative to the eNB frame are: the total length of the subframe−the offset of the RN frame relative to the eNB frame−a relay_physical downlink control channel R_PDCCH−a second idle time 3. In this method, since the offset of the RN frame relative to the eNB frame is too large, the relay link resources are reduced. In addition, the eNB considers by default the length of the PDCCH of the MBSFN subframe where the relay link of the RN is located to be a maximum value (2 OFDM symbols), so that the offset of the RN frame relative to the eNB frame is further increased, and the relay link resources are further decreased, thereby wasting the resources.